Electrode and electrochemical cell

ABSTRACT

An electrode, electrochemical cell, and electrochemical processes are disclosed. The electrode is a porous, multi-layered electrode which can have an element in flexible, strip form wound around a central, usually flat plate core, which core may serve as a current distributor. In any form, each layer can be represented by a very thin, highly flexible metal mesh. This can be a fine, as opposed to a coarse, mesh which has extremely thin strands and small voids. The electrode will have an active coating. For utilizing this electrode, the cell in one form will be a monopolar cell providing upward, parallel electrolyte flow through the porous, multi-layered electrode. A representative cell can have such electrode at least substantially filling an electrode chamber. The cells can be contained in a cell box that will provide the desired flow-through relationship for the electrolyte to the electrode. In cell operation, electrochemical processes which can be carried out include metal ion oxidation or reduction, oxidation of organic substituents, nitrate reduction as well as salt splitting.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 08/434,871, filed May 4,1995, now U.S. Pat. No. 4,783,050.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode, to an electrochemicalcell utilizing the electrode and to electrolyzer apparatus which canembody the cell. The electrode has a rigid core with, at least in part,a resilient surface. The electrode, also at least in part, ismulti-layered and porous. A representative electrochemical cellutilizing the electrode can include the electrode as anode, cathode orboth. Such a cell can be useful in reactions such as metal ion oxidationor reduction, or organic reactions, including destruction of organicspecies. The electrolyzer apparatus which may embody the cell may havespecial structure for separating anolyte from catholyte, and theelectrolyzer can include electrolyte recirculation. Usually, the cellwill be embodied in the electrolyzer in a monopolar format, although thepresent invention is not limited to the cell in any particulararrangement.

2. Description of the Related Art

It has been known to provide electrode structures in grid form, whichcan include pieces of expanded metal. The expanded metal pieces can belayered in sheets to provide a form like a laminate. For example, inBritish Patent No. 1,268,182, there is disclosed the layering of sheetsof expanded metal. An electrode of two to four sheets is taught, with anexemplary four sheet expanded copper mesh cathode used with a two sheetexpanded titanium mesh anode. The sheets may be of differing surfacearea, such as a sheet of smaller mesh sandwiched between two outersheets of larger mesh. For forming a composite electrode, a centralsolid plate can be utilized, preferably functioning as a bipolarelectrode.

Where a very short stack of two expanded metal plates is utilized, thiscan form a planar electrode. However, with a short stack, as taught inU.S. Pat. No. 4,097,347, a curved, cylindrical electrode may also beprovided. This has been taught to be useful, when employed as a cathode,for the electrolytic recovery of gold.

In an article of Pletcher et al, Journal of Applied Electrochemistry,No. 24 (1994), pages 95-106, there are disclosed three dimensionalnickel electrodes. They are more particularly depicted as a two stacktwin grid from expanded nickel, stacked nets from fine nickel mesh, anda stack of four nickel grids. These structures were chosen so as toconform to the available electrode space of a cell of standardconfiguration. The electrodes filled an electrolyte compartment of aparallel plate, laboratory-sized electrochemical reactor. These variousarrangements were found to be useful in testing the oxidation ofalcohols.

For utilization in a commercial operation, there has been taught thelayering of electrodes which can be superimposed expanded sheets. Thus,it is disclosed in U.S. Pat. No. 4,828,653 the usefulness of threeelectrode layers, which layers can vary, typically by geometry, so thatthe current density of each individual layer is substantially the same.Such a layered structure has serviceability as an anode for high-speedelectrogalvanizing processes.

Layering for electrode structure, again with non-uniformity of layers,has also been discussed in U.S. Pat. No. 4,761,216. Therein there isdisclosed a four layer electrode having a first layer support plate, asecond layer of woven screen mesh, or alternatively, fibers such asstainless steel fibers, a third layer required to be stainless steelfibers and a fourth layer of a mesh wire cloth. This structure isdiscussed as being useful in an electrochemical membrane cell.

Where electrode layers can be stacked wire screens, the utility of up to12 nested screens has been disclosed in U.S. Pat. No. 4,224,129. Such aconstruction, employed in a flow-through design, is taught as beinguseful for recovery of product from constituents in an electrolyte.

It would nevertheless still be desirable to provide a layered electrodewhere caution, as in nesting and stacking, can be obviated. It would bedesirable to provide such a layered electrode having ease and economy ofmanufacture, e.g., as by avoiding the alignment and "same size"considerations of stacked sheets or the fabrication of stacks of sheetsof differing geometry. It would also be desirable to provide such alayered electrode of simplistic construction avoiding the uniting offibers and meshes while still providing economy of manufacture coupledwith providing a great many layers, which multitude of layers could beselected within a wide range of layers, yet maintain ease and economy ofmanufacture regardless of selection.

Especially when dilute solutions are used as electrolyte, economic usageof cells for electrochemical processes can be limited because of thedifficulty encountered in achieving a high rate of transfer to electrodesurfaces. One dilute solution of interest is an electrolyte that isobtained as a scrubbing solution for removing oxides of nitrogen andsulfur from flue gases. The solution uses a ferrous chelate which isoxidized to an inactive ferric state. For re-use, this solution may beprocessed in an electrochemical cell. One approach for this solution ofparticular interest utilizes a plurality of cathode and anodecompartments separated by ion transfer membranes. Thus, it has beentaught in U.S. Pat. No. 4,126,529 to pass a spent scrubbing solutionthrough the cathode compartments of an electrochemical cell. Thecathodes are discussed as being a combination of a plate and wire mesh.The regeneration process not only provides for the reduction of thenonreactive ferric chelate to the reactive ferrous chelate, but also caninvolve the removal of sulfate ions from the scrubbing solution throughthe ion transfer membranes.

A recent development in regeneration of this electrolyte of particularinterest has focused, on the one hand, to maintaining the cell membrane,while on the other hand, enhancing electrode stability. Thus, it hasbeen shown in U.S. Pat. No. 5,320,816 that an otherwise unstable nickelor stainless steel anode material, is stable in the regeneration cellwhen a pH greater than 12 is maintained in the anode compartment.

It would, however, be desirable to provide for efficient spent scrubbingsolution regeneration without resort to special electrolyte control. Itwould be also desirable to achieve efficient regeneration whileproviding for ease and economy of cell operation and materials.

Where electrochemical cells embody a multitude of electrodes which mightbe useful for enhancing the rate for any mass transport limitedelectrochemical reaction, it has been known to space a multitude ofanodes and cathodes within a cell box. For example, in U.S. Pat. No.4,399,020 there has been disclosed a cell box containing a plurality ofanodes and cathodes where the electrolyte flows through the box, whichflow can include flow through a reticulate cathode. The reticulatecathodes for such an electrolyzer assembly may be metal foam cathodes.They may be provided with a porous plate support. Thus, it has beenshown in U.S. Pat. No. 4,515,672 to provide metallic foam cathodes onone or both sides of a porous support plate. These cathodes can then beemployed in a flow-through electrolyzer cell box assembly.

It would still be desirable to provide an electrolyzer cell boxcomprising enhanced operation of a mass transport limitedelectrochemical reaction which can be coupled with independent anolyteand catholyte flow. Or to provide such a cell having economy ofconstruction and operation, including economy of recycling electrolyte.

SUMMARY OF THE INVENTION

There is provided an electrode having as at least part of the electrodea multitude of expanded metal layers each of a fine, flexible mesh. Themesh has extremely thin strands and small voids like a window screen,but is preferably in expanded metal form. The layers of the mesh for theelectrode are tightly engaged one with the other in a face-to-facemechanical and electrical contact. As a full electrode structure, theelectrode has a rigid core with an autogenous, springy exterior. Thespringy exterior is provided by the multitude of fine mesh layers. Therigid core may be supplied by a material such as a coarse, or heavy,mesh.

The electrode structure may be prepared in a procedure involvingwrapping the mesh around the rigid core, the method involving multiplewrapping to provide the multiple layers. Where this core member of theelectrode structure comprises an at least substantially flat metal platemember having front and back major faces and an edge, the mesh wrap canbe expected to immediately mechanically engage the edge of the coreplate member. On the front and back major faces of the plate member,attachment can be subsequent to wrapping and can be such as by welding.

The invention also pertains to, generally, a cell embodying theelectrode. Particularly where the core member is elongated, and the meshwrapping covers only a portion of the core member surface, the coremember may serve as a current distributor for the electrode.Additionally, the core member can be coated, as on that part of itssurface area adjacent the mesh wrap, which core member coated surfacearea will serve as a part of the active electrode surface. A cellutilizing such electrode may be separated or unseparated. In a cell, thelayered electrode structure may serve as the anode or cathode or both.Because of the porosity of the electrode, it can be particularlyserviceable in a cell where an electrolyte will be conducted in aflow-through manner for the electrode. Such a cell might be useful, forexample, in metal ion oxidation or reduction, and organicelectrochemical reactions, including organic compound destruction. Othersuitable applications contemplated are salt splitting as well as nitratereduction.

Of particular interest is a cell for ferric ion reduction. Such a cellcan contain the layered electrode as cathode. It is also disclosedherein that such a cell of particular interest may successfully employan electrolyte permeable diaphragm.

There is also now disclosed an electrolyzer for containing theelectrolyte cells. Such electrolyzer has a cell box embodying overflowmeans as the electrolyte discharge. The cell box also has electrolyterecovery means. The recovery means can permit capture of the electrolyteoverflow for possible recycling. The cell box may be equipped withdouble tapered blocks for providing secure and efficient electricalconnection, between bus work external to the cell box, and theelectrodes of the electrolyzer cells. The cell box can also beconstructed to provide independent anolyte and catholyte flow. Thiscould be coupled with, for example, parallel catholyte flow through eachcatholyte chamber, as where such chambers contain the layered andporous, flow-through electrodes.

Thus, in one aspect the invention is directed to a porous, flow-through,fiber-free electrode comprising a rigid core member and autogenouslyspringy exterior wrapping member, which rigid core member comprises avalve metal reinforcement, which core member is in integral engagementwith an exterior wrapping member of a multitude of expanded valve metallayers from at least one continuous strip of valve metal mesh woundtightly around said core member, which mesh is a thin, highly flexiblemesh of extremely thin strands and small voids, the layers being tightlyengaged face-to-face contact with one another.

In another aspect, the invention is directed to the above-describedelectrode wherein the rigid electrode core can serve as a currentdistributor for the electrode as well as contributing, in part, to theactive electrode surface.

In another aspect, the invention is directed to an electrochemical cellfor metal ion oxidation or reduction comprising:

(a) a counter electrode;

(b) a diaphragm; and

(c) a working electrode of a porous, flow-through, fiber-free electrodecomprising a rigid core member and autogenously springy exteriorwrapping member, which rigid core member comprises a valve metalreinforcement, which core member is in integral engagement with anexterior wrapping member of a multitude of expanded valve metal layersfrom at least one continuous strip of valve metal mesh wound tightlyaround said core member, which mesh is a thin, highly flexible mesh ofextremely thin strands and small voids, the layers being tightly engagedface-to-face contact with one another.

In yet another aspect, the invention is directed to an electrolyzercomprising a nonconductive cell box having a floor and sides, said boxhaving electrolyte inlet means to pass electrolyte to electrodescontained in said box, electrolyte outlet means to conduct electrolyteaway from said cell box, said box containing a plurality of anodes andcathodes and means spacing said anodes and cathodes within said cellbox, with there being anode and cathode bus bars located externally ofsaid cell box, the improvement comprising:

(a) electrolyte outlet means at a top edge of at least one side of saidbox and comprising overflow troughs positioned externally to the cellbox; and

(b) electrolyte inlet means comprising means introducing electrolyte atleast substantially at the floor of said cell box providing for upwardflow of said electrolyte through chambers within said cell box.

In an aspect of the invention pertaining to the electrolyzer, there canbe associated with the electrolyzer:

(a) bus bars on said cell box having notches at the upper edge of saidbus bars, said notches being configured for having conductor bars fromsaid anodes and said cathodes inserted into said notches; and

(b) a double tapered block inserted within at least one of said bus barnotches, said blocks having opposed tapered mating faces which whenbrought together by compression provide a formed bus block unit havingmajor faces at each side of the block unit, with each major faceproviding contact between the bus block unit and an electrode conductorbar.

Another aspect of the invention pertains to an electrolyte process thatincludes establishing the above-described porous electrode in anelectrolyte cell.

In a still further aspect, the invention is directed to anelectrochemical cell for carrying out electrochemical ferric ionreduction where the cell comprises, as a cathode, the hereinbeforedescribed layered electrode, which cathode operates at a positivepotential of about +0.1 volt versus a normal hydrogen electrode wherethe current efficiency is 100%.

The invention in an additional aspect is directed to an electrolyticprocess providing metal ion reduction by electrochemical reaction. Inthis process, there can be used a dimensionally stable anode and anolytecan be circulated to the anolyte chamber containing this anode, whichanolyte is different from the catholyte. The catholyte can contain themetal ion oxidation species and this can be circulated to a catholytechamber containing the hereinabove described electrode as cathode.

Another aspect of the invention is the electrolytic process providingmetal ion oxidation or reduction by electrochemical reaction, whichprocess comprises:

(a) establishing a counter electrode chamber having a cathode electrodetherein;

(b) providing electrolyte to said counter electrode chamber, saidelectrolyte being free from metal ion for oxidation or reduction;

(c) providing a diaphragm separating said counter electrode chamber froma working electrode chamber;

(d) establishing said working electrode chamber with a porous,flow-through, fiber-free electrode comprising a rigid core member andautogenously springy exterior wrapping member, which rigid core membercomprises a valve metal reinforcement, which core member is in integralengagement with an exterior wrapping member of a multitude of expandedvalve metal layers from at least one continuous strip of valve metalmesh wound tightly around said core member, which mesh is a thin, highlyflexible mesh of extremely thin strands and small voids, the layersbeing tightly engaged face-to-face contact with one another; and

(e) circulating electrolyte to said working electrode chamber, saidelectrolyte containing metal ion for oxidation or reduction.

A still further invention aspect is the method of manufacturing anelectrode for electrochemical processes, which electrode comprises arigid elongated valve metal core member and an autogenously springyelectrode exterior valve metal wrapping member comprising at least onecontinuously flexible strip of valve metal mesh, which method comprises:

(a) wrapping said flexible strip of valve metal mesh around at least aportion of said rigid core member in a multitude of wrappings layeredone atop the other, providing contact between said strip and said coremember at the wrapped edges of said core member; while,

(b) permitting flexing of said flexible strip away from wrapped broadsurfaces of said core member;

(c) flexing said flexible strip onto said wrapped broad surfaces of saidcore member; and

(d) securing said flexible strip in flexed form in secure, electricallyconductive contact with said broad surfaces of said core member.

The invention is also directed to a bipolar electrode where one side ofthe electrode has the hereinabove described flexible mesh screen layersand the other side, e.g., a back major face of a metal plate electrode,can serve, as the electrode of different polarity. Such back major facemay contain surface enhancement such as by plasma spraying a metal ormetal oxide onto the surface.

The electrode of the invention can utilize readily, commerciallyavailable materials in its construction. It can provide for economy byavoiding other materials which may be utilized for manufacturing ormaking high surface electrodes, such as expensive porous titanium asexemplified by sintered titanium particles, or fiber mats. In additionto being economical, the layered electrode readily overcomes anydifficulty associated with other high surface area electrodes. Thus, theelectrode is fiber-free, for example it is not a felted mat or astitched fiber fill where difficulty can be encountered during attachingof current collectors and/or support frames.

The electrode can also permit the area to volume ratio to be readilyadjusted, such as by controlling the parameter of the number ofindividual layers, which can include selecting the optimum number oflayers. The electrode lends itself readily to straightforward weldingtechniques for attaching the springy layers to a rigid core. Coatingscan be applied to both the core as well as the layers, enhancing theelectrocatalytically active surface of the electrode. By retaining anautogenous, springy exterior, the electrode provides tolerance reliefwhen pressed against a separator.

The electrode can provide demonstrably high current efficiencies. Thesecan be achieved even where the electrode will serve as a cathode atpositive potential, e.g., above +0.1 volt. The high surface area of theelectrode allows the electrode to operate at elevated current densitiesbased on the geometric area of the electrode. However, the real currentdensities can be below the limiting current densities of reactions whichthus could not be handled without the special layered electrode.Moreover, it has been found that the reducing of this real currentdensity can be accompanied by an enhancement in current efficiency. Forexample, reduction of ferric to ferrous ion for a layered cathodeoperating at 35 amperes per square foot has been found to operate at acurrent efficiency of near 100 percent for ferric ion concentrations inexcess of 750 milligrams per liter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section of a preferred metal mesh, shown actual size.

FIG. 1A is a portion of the mesh of FIG. 1, shown greatly enlarged.

FIG. 2 is a front view of an electrode structure having the mesh screenof FIG. 1 wrapped many times around a flat, rigid core mesh in plateform.

FIG. 2A is a front view of an electrode structure having two meshscreens wrapped around a mid-portion of a core in plate form.

FIG. 2B is a front view of two electrodes of FIG. 2 brought together toform an enlarged electrode structure.

FIG. 3 is an exploded perspective view, in partial cutaway, of anelectrolyzer utilizing the electrodes of FIG. 3.

FIG. 3A is an enlarged perspective view of a portion of the bus barassembly for a cell box.

FIG. 3B is an enlarged perspective view of an electrode frame for a cellbox.

FIG. 4 is an enlarged partial elevation sectional view of a monopolarcell for use in the electrolyzer of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The metals of the electrode will most always be valve metals, includingtitanium, tantalum, aluminum, zirconium and niobium, although the use ofother metals is contemplated, e.g., nickel and steel. Of particularinterest for its ruggedness, corrosion resistance and availability istitanium. As well as the normally available elemental metals themselves,the suitable metals of the substrate can include metal alloys andintermetallic mixtures, as well as ceramics and cermets such as containone or more valve metals. For example, titanium may be alloyed withnickel, cobalt, iron, manganese or copper. More specifically, grade 5titanium may include up to 6.75 weight percent aluminum and 4.5 weightpercent vanadium, grade 6 up to 6 percent aluminum and 3 percent tin,grade 7 up to 0.25 weight percent palladium, grade 10, from 10 to 13weight percent plus 4.5 to 7.6 weight percent zirconium and so on.

By use of elemental metals, it is most particularly meant the metals intheir normally available condition, i.e., having minor amounts ofimpurities. Thus, for the metal of particular interest, i.e., titanium,various grades of the metal are available including those in which otherconstituents may be alloys or alloys plus impurities. Grades of titaniumhave been more specifically set forth in the standard specifications fortitanium detailed in ASTM B 265-79.

The representative metal titanium can be made in foil form and the foilexpanded to prepare the mesh. The mesh can be useful in the formprovided by the metal expander, or it may be flattened after expansion,e.g., to enhance springiness of the mesh. A typical resulting expandedmetal mesh, having dimensions which can be associated with those of awindow screen, is shown in FIG. 1. The mesh of FIG. 1, designated in thefigure as the mesh 1, has been expanded from a metal foil. In theexpansion there has been provided substantially rhombus shaped voids,and the void pattern is outlined in a continuous network of metalstrands. The thickness of the starting metal foil can be quite small,e.g., on the order of about 0.005 inch, resulting in a mesh, sometimesreferred to herein for convenience just as a "mesh screen" of the same0.005 inch thickness. Generally, the mesh will have a thickness withinthe range of about 0.0025 inch to about 0.025 inch. Within this range ofthickness, the mesh will be highly flexible, which is desirable not onlyfor manufacture of the electrode but for characteristics of theelectrode, both of which will be discussed hereinbelow. The mesh canhave fineness like a window screen, although when it is expanded from afoil of metal, it is a continuous network of strands and not a wovenwire screen. The form of the continuous network of strands is preferredfor economy, although utilization of a mesh in screen form which is awoven wire screen, is also contemplated.

The mesh screen will have a small mass to volume. It will also have ahigh surface area to volume ratio. Such a ratio can be above about 50,but is more typically on the order of 60-80, square centimeters percubic centimeter or more.

Referring then to FIG. 1A, it will be seen that this mesh 1 has strands2 which interconnect at nodes 3. For this mesh in its normal size, theactual size of which has been shown in FIG. 1, the strands 2 will have awidth within the range from about 0.003 inch to about 0.012 inch, with amesh of strand width of 0.007 inch being shown in FIG. 1. The thicknessof the strands 2 is the thickness of the mesh screen, or original foil,i.e., for the mesh of FIG. 1, the strands 2 have a thickness of about0.005 inch. The nodes 3 are double strand thickness, about 0.014 inchthick. The strands and nodes are separated by a "void" or "rhombusaperture". It will be understood that this void could be of differingshape, e.g., diamond-shaped. Each void, as shown in FIG. 1A, has a shortway of design, or SWD dimension, as well as a long way of design, or LWDdimension. For the mesh screen shown in actual size in FIG. 1, the SWDdimension is typically within the range from about 0.04 inch to about0.08 inch, and as shown is about 0.06 inch. The LWD dimension for thevoids of this screen is advantageously, for desirable surface area tovolume ratio for the screen combined with desirable flexibility andautogenous springiness of the screen, within the range from about 0.1inch to about 0.15 inch, and is about 0.125 inch for the screen ofFIG. 1. Such dimensions, besides providing for great flexibility for themesh screen, provide for coilability of the screen, which may also bereferred to herein as wrapping of the screen, and will be discussed moreparticularly hereinbelow, as well as providing for screenstretchability.

Referring then to FIG. 2, an electrode 5 has mesh 1, shown in wrappedform, providing a multitude of mesh screen layers, around an expandedmetal electrode core 4. This electrode core 4 as depicted in the figureis an expanded metal core having a continuous network of metal strandsconnected at nodes. However, it is contemplated that the core 4 may beof other structure, e.g., a solid plate or a foam metal core. Ingeneral, it is advantageous that the core 4 be neither flexible,coilable nor stretchable. Thereby the core 4 can serve to contributerigidity to the electrode 5 which may also be termed herein the"electrode structure". By use of the term "electrode structure" herein,it is meant an article which can serve as an electrode, but is not asingle item, and is represented by the electrode structure 5 of thisFIG. 2, which structure is a combination of the mesh 1 and core 4. Itmay also refer to such a structure where a part of the structure canserve as a current distributor for the electrode. For simplicity, thestructure is usually referred to herein merely as the "electrode".

Although the core 4 shown in FIG. 2 is plate-shaped, i.e., has front andback major faces and an edge, other forms for the core 4 arecontemplated, such as rods, tubes and rectangular channels. For thespecific core 4 depicted in FIG. 2, this core 4 is of 24 gauge metal,providing a thickness for the core of 0.025 inch, which metal has beenexpanded to provide voids. For large scale commercial operations it iscontemplated that an expanded metal mesh core 4 may have a thicknesswithin the range of from about 0.02 inch to about 0.25 inch or more. Thecore 4 in addition to providing rigid reinforcement for the electrodestructure 5 can be serviceable for current distribution. For example,the top edge 10 of the core 4 may have affixed thereto a conductor bar(not shown) for conducting electric current to the core 4, which thencarries the current on down to the mesh 1. Thus the core 4 provides easeof connection for the electrode structure 5 for current distribution.Moreover, the bottom portion of the core 4 as shown in FIG. 2, i.e., theportion masked by the mesh 1, may contain a coating. It is contemplatedthat such a coating could be extended to cover the entire area of thecore 4, if desired. Thus, where the core 4 is connected to currentdistribution means, and is coated, the core 4 can serve as a currentdistributor, as well as serve as part of the electrode active area.Where reference is made herein to the top or bottom of FIG. 2, it is tobe understood that the usual orientation of the electrode structure 5 ofthe figure is in an upright manner as shown in FIG. 2. However, it iscontemplated that other orientation of electrode structure 5 may beuseful and thus reference terms as top and bottom are only used hereinfor convenience.

By providing many layers of the mesh 1 around the electrode core 4, themesh 1 extends the active area of the electrode outwardly in allhorizontal directions from the core 4. Moreover, the layers all being ofthe same mesh 1, each individual layer has the same uniform porosity,although other structure is contemplated. The core 4 has a bottom edge9. The bottom edge 9 of the core 4 and of the mesh 1 are coextensive forthe electrode structure 5. However, such construction need not always beused. Thus the core 4 may extend downwardly into the mesh 1 someselected portion only of the height of the mesh 1, but which extensionfalls short of extending completely to the bottom of the mesh 1. Also,the bottom edge 9 of the core 4 may extend beyond the mesh 1 (asdepicted in FIG. 4). Moreover, the core 4 need not be uniform. Forexample, the top portion of the core 4 above the top edge of the mesh 1might be a solid plate, whereas the portion of the core 4 underneath themesh 1 might be in expanded metal form as shown in the figure, toaugment circulation of electrolyte through the electrode structure 5.Furthermore, the core 4 in the form of a flat plate could have fullplate extension under the mesh 1, but above the mesh 1, the core 4 couldneck down whereby the top portion of the core 4 could be more in stripshape, i.e., the shape of a conductor bar. Metallurgical differences forthe core 4 can include a titanium-palladium alloy for the upper portionof the core 4, with a titanium lower portion under the mesh 1. The core4 can also be a composite metal represented by a titanium sheet surfacebonded to a copper core. Further in this regard, it is contemplated thatthe mesh can be a different valve metal than the core 4.

The mesh 1 by extending horizontally outwardly in all directions fromthe core 4 forms a mesh extension 6 at each vertical edge of the core 4.Thus the mesh 1 extends the active area for the electrode beyond thevertical edge 7 of the core 4 at the top edge 8 of the mesh 1. For manyof the applications wherein the electrode structure 5 of FIG. 2 will beutilized, there will be from about 2 to about 50 layers of a mesh 1 suchas shown in FIG. 1 provided on the electrode core 4. Using less thanabout 2 layers of the FIG. 1 mesh 1 on the core 4 will usually beinsufficient for achieving desirable current efficiency for theelectrode 5. While greater than about 50 layers of the mesh 1 of FIG. 1can provide for difficulty in attaching the mesh 1 to the core 4, e.g.,tearing of the mesh 1 during spot welding attachment. Such a range oflayers can provide for the mesh 1 extending outwardly from the core 4 ata thickness within the range from about 0.1 inch to about 0.25 inch.Usually, for economy of electrode structure, combined with desirableefficiency of operation as well as manufacture, the electrode 5 willcontain more than 5 and advantageously for enhanced current efficiencymore than about 10, up to about 30 layers of the FIG. 1 mesh 1 on thecore 4. Generally, all of the individual layers of the mesh 1 will bethe same mesh. However, different structures are contemplated.

Although the height of the mesh 1 in FIG. 2 has been shown to cover asubstantial portion of the core 4, such structure need not always beutilized. Thus the height of the mesh 1 on the core 4 may extend no morethan 50 percent or even less up the height of the core 4 for providingthe electrode structure 5. It will be appreciated that the actualconstruction will be dependent upon cell design and electrode use. It iscontemplated that all of the electrode structure 5 of FIG. 2 will beelectrically conductive. That is, the FIG. 2 electrode structure will beinsulation-free. By being insulation-free, it is meant to includefreedom from any insulation layers, either between the core 4 and themesh 1, or between the individual layers of the mesh 1 or as an outerlayer for the mesh 1.

For the electrode structure 5 the mesh 1 will advantageously provide aspecific area for the mesh 1 within the range from about 250 squareinches per square foot to about 6,000 square inches per square foot. Forexample, a one square foot sample of a single layer of mesh, having atotal surface area for all of the strands and nodes of the sample of 100square inches, when supplied as 50 layers of the mesh, will provide aspecific area of 5,000 square inches per square foot. Less than about250 square inches per square foot will be generally insufficient forachieving enhanced current efficiency in electrode operation, whereasgreater than about 6,000 square inches per square foot can beundesirable because of economy, as well as because of difficulty inelectrode fabrication. Moreover, as mentioned hereinabove, this meshportion of the electrode structure 5 can preferably have a surface areato volume ratio of greater than about 50 square centimeters per cubiccentimeter. This elevated surface area to volume ratio is desirable forenhanced current efficiency in a minimum electrode volume. As will benoted by reference to FIG. 2, the electrode structure 5 of the inventionoffers a variety of considerations for electrolyte flow with respect tothe electrode structure 5. For example, the electrolyte may be fed fromthe bottom edge 9 of the electrode 5 to percolate upwardly through themesh 1. That is, in this regime the electrolyte flows along the generalplane of the core 4. Conversely, electrolyte feed can come from adjacentthe top edge 8 of the mesh 1, whereby the electrolyte can cascade downthrough the mesh 1. A porous core 4, e.g., as a perforated plate,expanded metal mesh, foamed metal, parallel rods, blades spaced apartfrom one another, or perforated tubes, can enhance electrolyte flowdistribution. Such a porous core 4 can also permit electrolyte flowthrough the electrode 5, i.e., horizontally or transverse to the generalplane of the electrode core 4 as shown in the figure. The electrodestructure 5 as contemplated is designed to be a flow-through electrode,as opposed to a flow-by electrode where electrolyte typically only flowsby a solid face of an electrode. The flow-through aspects of theelectrode structure 5 come into play whether the electrolyte ispercolating upwardly, cascading downwardly, or flowing through theelectrode structure 5.

For ease of manufacture, the electrode structure 5 of FIG. 2 can be madeby wrapping a sheet of mesh 1 around the core 4. For example, a smallinitial portion of the starting edge of the mesh 1 can be bent around avertical edge 7 of the core 4 and then the mesh 1 continuously wrappedaround the core 4 until the desired number of layers have been achieved.This wrapping means of manufacture will provide good initial physicalcontact of the mesh 1 with the vertical edges 7 of the core 4. Where themesh 1 is springy, the mesh 1 in freshly wrapped form, particularly onthe front and back major faces of the core 4, can have slight flexingaway from the surface of the core 4. Thus, in subsequent affixing of themesh 1 to the core 4, the mesh 1 is flexed onto the exterior surface ofthe core 4 and secured thereto. Securing can be by any means generallyuseful for providing adhering of metal-to-metal in good electricalcontact. Initially, the starting edge of the mesh 1 may be crimped toassist in engaging the start of the mesh 1 with the edge 7 of the core.In general, crimping of the mesh 1 is contemplated, particularly forfirm engagement with the core edges 7. Preferably, the securing will beaccomplished by welding the mesh 1 to the core 4, e.g., at selectedspots 11, or by seam welding, or arc welding. Other securing meansinclude rivets, bolts and twisted wire. Where welding is used, spotwelding is preferred for efficiency and economy. However, where thefinal edge of the mesh wrap can create a rough surface, seam welding maybe utilized to provide a smooth finished exterior mesh surface.

Particularly when spot welding is employed, only a few spots 11 arenecessary between the mesh 1 and the core 4 for providing a secure bondof the mesh 1 to the core 4, coupled with efficient currentdistribution. Since much of the area of the mesh 1 in spot welding isnot directly secured to the mesh 4, usually 99% is not welded, orconversely, less than 1% of the area of the mesh, and typically on theorder of 0.5%, is welded, the major exterior areas of the mesh 1maintain a characteristic of autogenous springiness, e.g., the mesh 1 issusceptible to flexing inwardly toward the inner core 4, such as bymanual pressure. This springiness can be highly desirable formaintaining a low electrolyte pressure drop as electrolyte cascadesdownwardly or percolates upwardly through the layers of the mesh 1.Autogenous springiness is further desirable for contributing sufficientresilience to the mesh 1 for retarding permanent electrode deformation.Such springiness can also desirably provide tolerance relief when themesh 1 is compressed against an opposing surface such as a separator. Byhaving such a springiness characteristic, the mesh 1 adjusts for anyunevenness that might be present in the opposing surface, e.g., providea zero gap between the mesh 1 and a separator.

Where the electrode structure 5 has been prepared by winding the mesh 1around the core 4, and typically after the mesh 1 has been secured tothe core 4, some further manufacturing steps can be undertaken. Forexample, if the mesh 1 were to only be present on the front broad face12 of a flat plate core 4, the mesh 1 could be stripped away from theback face of the core 4 and, optionally trimmed away from the verticaledges 7 of the core 4. Alternatively, for forming this multitude oflayers, which could be formed on only one broad face of the core 4, themesh 1 could be first wrapped around a mandrel. The mandrel could be thesame size or larger or smaller, than the core 4 which will be eventuallyused. The mesh 1 wrapping around the mandrel can then be slipped fromthe mandrel and the resulting continuous strip of mesh, maintained infolded condition, could be compressed against a broad face 12 of thecore 4. This could provide a structure having a mesh 1 only on one faceof the core 4, or a second winding from the mandrel can be used infolded form and compressed against an additional broad face 12 of thecore 4. Such technique could include extended mesh extensions 6 beyondthe vertical edges 7 of the core 4. These mesh extensions 6, where thesemeshes 1 are on both the broad front face 12 and back face of the core4, could be sufficiently extended to themselves be secured together toone another, without securing to the plate 4, such as by spot welding.

Rather than attaching a folded continuous compressed strip, such asprovided from a mandrel, directly to the core 4, the core 4 can firsthave a number of windings of the mesh 1 around the core 4. Then theadditional mesh from the mandrel could be placed upon these initialwindings to provide further layers of the mesh 1 on the core 4. Suchtechnique is useful, as for example in providing a seamless face to themesh 1. In this technique, the folded strip from the mandrel can havethe finishing edge of the strip positioned face down against the core 4,or against any mesh 1 which has been prewrapped on the core 4. In thisway, the projected face of the mesh 1 will provide a seamless face.

Where a structure has a mesh 1 only on one face of the core 4, such canbe utilized for preparing a bipolar electrode. For example, a broadfront face of the core 4 can have a multiple layer mesh 1 serving as acathode. Then the broad back face of the core 4 could be a plate anode.If the faces are coated, differing coatings can be used on the frontmesh and on the back face. The mesh, as well as the core 4, ispreferably an expanded titanium metal mesh.

As will be noted in FIG. 2, the mesh 1 is typically a wide band of mesh1 from the bottom edge 9 to the top edge 8. However, other structuresare contemplated.

Referring then to FIG. 2A, there are two narrow strips of mesh 1, moreparticularly an upper mesh strip 13 and a lower mesh strip 14. Thesemesh strips 13, 14 are wound around the electrode core 4 in the manneras described herein to provide mesh layers as described herein. The meshstrips 13, 14 are wrapped tightly adjacent one another so to be inedge-to-edge contact at their common edge 15. The bottom edge 9 of thelower mesh strip 14 is above the bottom of the core 4, exposing a lowercore section 16. As with the mesh 1 in FIG. 2, the mesh 1 in this FIG.2A extends outwardly from the vertical edge 7 of the core 4. This formsa mesh extension 6 at both vertical edges 7 of the core 4 for both theupper mesh strip 13 and lower mesh strip 14. Each mesh strip 13, 14 issecured to the core 4 by welding at spots 11. Although upper and lowermesh strips 13, 14 have been shown, it will be understood that amultitude of narrow strips could be positioned edge-to-edge as in FIG.2A along the core 4 so that the mesh 1 is segmented into many adjacentnarrow strips, e.g., four to six strips or more. However, for economy ofmanufacture, a non-segmented mesh 1 is often advantageous.

Referring then to FIG. 2B, there is depicted an electrode 5 having mesh1, shown in wrapped form providing a multitude of mesh screen layers,around two electrode cores 4A, 4B, placed beside one another. For thiselectrode 5, two of the electrodes of FIG. 2 have been brought togetherside by side, each forming an electrode panel 17, 18. These panels 17,18 are in edge-to-edge contact along a common edge 19 of the mesh 1 foreach panel. By abutting the panels 17, 18 at the common mesh edge 19,the panel electrode cores 4A, 4B are spaced apart at their commonvertical edge 7. This spacing 90 at the common vertical edges 7 isoccasioned by the mesh 1 having a mesh extension 6 that extendsoutwardly beyond the vertical edge 7 of each of the electrode panels 17,18. It will be understood that the electrode panels 17, 18 may bebrought together to form the electrode 5 by any convenient means, e.g.,a current distributor strip (not shown) running across the entire topedge 10 of each core panel 4A, 4B. By means such as shown in this FIG.2B, large panel electrodes 5 can be formed by bringing togetherindividual, common smaller electrode panels 17, 18 whereby the finishedelectrode 5 can have segmented electrode cores 4A, 4B. Additionally, insuch a panel 5, the meshes 1 may be segmented, as being in separatestrip form as the upper and lower mesh strips 13, 14 of FIG. 2A. Suchstrip form meshes might be useful on either of the electrode panels 17,18. Other variations are contemplated. For example, the mesh on oneelectrode panel 17 could be upper and lower strips 13 and 14 (FIG. 2A)while the mesh on an other, adjacent electrode panel 18 could be amesh 1. Or the mesh of one panel 17 could have reduced height, such asthe only and upper mesh strip 13 (FIG. 2A) whereas the mesh 1 on anadjacent electrode panel 18 could be an extended mesh 1 as shown in FIG.2B. Or the electrode panels 17, 18 could themselves be segmented, forexample they could each be in vertical, spaced apart, strips, orsegments connected at one or more edges, such as the top edge, by acurrent distributor strip also functioning to provide support to thepanel.

The electrode 5 will be useful in electrochemical cells as describedmore particularly hereinafter. These cells can be utilized inelectrolyzers for conducting electrochemical reactions. An electrolyzerof particular interest is depicted in the figures.

Referring then to FIG. 3, an electrolyzer 20 of particular interest aswell as being representative of one aspect of the present inventioncomprises a cell box of, generally, a floor 28, side walls 33,34, frontplate 21, and back plate, not shown. The cell box is equipped withfeed/discharge, or front, assembly 30. This front assembly 30 has frontplate 21. Connecting through the outer plate 21 is a catholyte dischargeport 23, an anolyte feed port 24, a catholyte feed port 25, a tank drain26 and an anolyte discharge port 27. Behind the outer plate 21, theanolyte feed port 24 connects with an anolyte feed manifold, made insections 32, which extend into the electrolyzer 20. The catholyte feedport 25 connects through the front plate 21 to the catholyte feedmanifold 31, which manifold 31 protrudes through the separator plate 39into the electrolyzer 20. The bottom of the electrolyzer 20 has a floor28. Electrolyte can be drained through the tank drain 26 located at theelevation of the floor 28.

The electrolyzer 20 is equipped with monopolar cells 40. Each monopolarcell 40 has a cathode structure 41 and on each side of the cathodestructure 41 are anode structures 42, 43. The cathode structure 41 has acathode conductor bar 44, current distributing mesh 45 and high surfacearea cathode mesh 46. Between the cathode structure 41 and each anodestructure 42, 43 is a separator 47. The separator 47 is in two sections,with one section removed, and both sections broken away to expose anunderlying anode frame grid 57. The separator 47 separates the cathodemesh 46 from an anode 48, each anode 48 being contained in an anodeframe 49. Each anode 48 has an anode conductor bar 50, an anode mesh 51as well as anode guide slots 52.

As shown most particularly in FIG. 3B, the anode frame 49 has two outerplates 53. Between these outer plates 53 is an anode frame slot 55 (FIG.3) which terminates at an upper outer edge in an anode discharge spout56. Each anode outer plate 53 contains an anode frame grid 57. As willbe noted in FIG. 3B, each anode frame grid 57 is made up of a series ofvertical support strips 81 which intersect a series of parallelhorizontal support strips 82 with a central principal support strip 83.These intersecting strips 81, 82 form the voids 84 of the grid 57. Thetotal area of this grid 57 is sized to match the total planar face areaof the anode mesh 51, and matches at least a portion of the total planarface of the cathode mesh 46. The anode guide bars 52 of the anode mesh51 slip into guide slots 80 in the anode frame 49 and frame grid 57 whenthe anode 48 slides into the anode frame slot 55. These slots 80position the anode 48 within the anode frame 49. At the bottom of theinner plate 54 is an anolyte feed manifold section 32. This manifold notonly distributes anolyte but also houses a tie rod 85. At essentiallyeach edge of the anode frame outer plate 53 there is a tube section 75through which locating rods 58 pass. These tube sections 75 serve asseparators between the outer plates 53 of adjacent anodes. Also, it willbe understood that the anolyte feed manifold sections 32 connecttogether in series for forming the anolyte manifold 73 (FIG. 4).

On the other side of the cathode structure, from the anode structure 43is a second anode structure 42. These structures are identical to eachother. For example, the anode structure 42 likewise has an outer plates53 and inner plate 54 which terminate in their upper direction at oneouter edge in an anode discharge spout 56. An anolyte feed manifoldsection 32 provides a conduit for feeding electrolyte to each anodeframe slot 55 by means of orifices (not shown) for discharging anolytefrom the anolyte feed manifold into each slot 55. Each monopolar cell 40has the anode structures 42, 43 and cathode structure 41 maintained inalignment by anode locating rods 58.

Cathode structures 41 positioned front to back are separated by an anodeseparator plate 39. Just inside the electrolyzer inner plate 22, therecan be positioned a cathode structure 41. The electrolyzer side wall 33has an anolyte discharge trough 35 which is positioned under the anodedischarge spouts 56 of the anode frames. This anolyte discharge trough35 connects at the electrolyzer outer plate 21 with the anolytedischarge port 27. On the other side of the electrolyzer 20 theelectrolyzer side wall 34 has a catholyte discharge trough 36. Catholyteoverflowing the top edge 77 of the side wall 34 enters the catholytedischarge trough 36. This catholyte discharge trough 36 connects at theelectrolyzer outer plate 21 with the catholyte discharge port 23. Forconvenience, as mentioned hereinbefore, the portion of the electrolyzerhousing defined by the floor 28, side walls 33, 34, front plate 21 and aback plate (not shown) is sometimes referred to herein as the "cellbox". Thus the discharge troughs 35, 36 are positioned outside the cellbox.

Positioned outside each discharge trough 35, 36 and thus outside theelectrolyzer 20 on each side of the electrolyzer 20, is an electricalbus assembly 60. This assembly 60 has an outer plate 61 and inner plate62 for enhanced heat dissipation. These plates are separated, also forcooling. The electrical bus assembly 60 depicted in FIG. 3 connects withthe anode conductor bars 50 through the portion of these bars 50 whichextend beyond the anode mesh 51 and thus beyond the electrolyzer 20 aswell as extending over the anolyte discharge trough 35. At the uppermostedge of the electrical bus assembly 60 along the anolyte dischargetrough 35, the inner and the outer bus plates 61, 62 have notches 63.Each notch 63 is utilized for connecting a pair of anode conductor bars50 using double tapered blocks, in a manner as more particularly shownin FIG. 3A.

Referring then to FIG. 3A, each notch 63 of the outer and inner busplates 61, 62 contains double tapered blocks of a floating, tapered busblock 64 and a fixed tapered bus block 65. These bus blocks 64, 65 aresecured together by a bolt 66 and nut 67. When joined together, thejoined bus block 70 has spaces 68 between the bus block 70 and plateprojection 71 for both the inner and outer plates 62, 61. These spaces68 provide room for the extension sections of the anode conductor bars50.

In assembly, an anode conductor bar 50 is positioned in a slot 68 oneach side of a bus block 70 while the tapered bus block members 64, 65are in loose fit condition. The bolt 66 is then tightened against thenut 67, forcing the floating tapered bus block member 64 against thefixed tapered bus block member 65. This tightening exerts a wedgedcompression of the bus block members 64, 65 against the anode conductorbar 50 extension sections. This compression tightly engages these anodeconductor bar 50 extension sections with the plate projections 71 withinthe spaces 68.

Referring then to FIG. 4, there is shown a cathode separator plate 39against which there is positioned a cathode structure 41. On theopposite side of the cathode structure 41 from the separator plate 39 isa separator 47. The separator 47 is positioned up against one anodeframe plate 53. On the other side of this one anode front plate 53 fromthe separator 47 is an anode frame slot 55. This slot 55 then has oneach side an anode frame plate 53. Continuing from left to right in FIG.4 from this anode frame plate 53, there is shown a separator 47, cathodestructure 41, cathode separator plate 39, another cathode structure 41,separator 47, anode frame plate 53, anode frame slot 55, anode frameplate 53 and separator 47. For each cathode structure 41 shown, thecathode core 4 extends below the electrode mesh 1. Connecting with eachanode frame slot 55 is an anolyte feed slot 72 connecting from theanolyte feed manifold 73. Within the feed manifold 73 is a tie rod 85.The feed manifold 73 terminates in an end cap 75. As will be seenparticularly by reference to this FIG. 4, an electrolyzer 20 which isrepresentative of the present invention can be constructed so as toseparate anolyte and catholyte. Thus, differing anolyte and catholytesubstituencies can be utilized in the electrolyzer 20 without concernfor mixing.

In operation for the electrolyzer 20, catholyte feeding from a sourcenot shown feeds through the catholyte feed port 25 into the catholytefeed manifold 31. From this manifold 31 catholyte exits the manifold 31through the orifices 76 into catholyte feed chambers (not shown) fromwhich the catholyte percolates upwardly through the cathode mesh 46. Atthe top of the side wall 34, catholyte overflows the top edge 77 intothe catholyte discharge trough 36. From this trough 36 catholyte isdischarged from the electrolyzer 20 through the catholyte discharge 23.

Anolyte for the electrolyzer 20 enters through the anolyte feed port 24into the anolyte feed manifold 73. The anolyte feed manifold for thisrepresentative electrolyzer is designed smaller than the catholyte feedmanifold because anolyte flow rates are lower than the catholyte ratesfor the specific, expected use of the cell. From the anolyte feedmanifold 73 anolyte is fed through anolyte feed slots 72 into the anodeframe slots 55. Therein the anolyte percolates upwardly between pairs ofanode frame plates 53 and past the anode frame grids 57. From the top ofthe anode frame 49, anolyte passes from the anode discharge spout 56 tothe anolyte discharge trough 35. Spent anolyte then exits theelectrolyzer from the trough 35 through the anolyte discharge port 27.It may be desirable to equip the electrolyzer 20 with a hood (notshown).

Electrical connections for the anode electrical bus assembly 60 are madethrough the bus plates 61, 62 to an electrical source (not shown).Current is distributed from the bus assembly 60 through the anodeconductor bars to the anode 48. In similar manner, current is conductedby the cathode conductor bars 44 to a cathode bus assembly (not shown)which is further connected to a source of electrical energy (not shown).

In assembly, the basic housing structure of the electrolyzer 20including the floor 28, side walls 33, 34 and front plate 21 and backplate (not shown) are assembled. During this assembly, the catholytefeed manifold 31 is installed. Outside of the basic housing of theelectrolyzer 20 on the side walls 33 there are installed the electrolytedischarge troughs 35, 36. Exterior of these troughs 35, 36 there isplaced the anode electrical bus assemblies 60 and cathode bus assemblies(not shown). Then within the basic housing of the electrolyzer the cellsare assembled by inserting cathode structures 41, cathode separatorplates 39, anode structures 43, which anode structures 43 haveseparators 47 adhered thereto, into the inner cavity of the basichousing of electrolyzer 20. For this representative electrolyzer, thecells 40 are formed by the continuous sequence of elements arranged inthe manner as shown most particularly in FIG. 4. During this part of theassembly, the anolyte feed manifold sections 32 are brought intoconformity for providing the interior anolyte feed manifold 73. In thispart of the assembly, the anode frames 49 are inserted with connectingtube spacers 75 and the anode locating rods 58 are passed through thesetube spacers 75 to provide anode frame alignment throughout theelectrolyzer 20. Following this alignment, the anodes 48 can be insertedin the anode frames 49, care being taken to insert the anode slots 52within the anode guide bars 80.

As cathode structures 41 and anodes 48 are inserted, the extensionsections of their respective conductor bars 44, 50 are spaced withinslots 68 of electrical bus assemblies 60 adjacent bus blocks 70 whichare in loose connection. Following this, the tapered bus block members64, 65 are bolted tightly together to firmly engage the extensionsections of the conductor bars 44, 50 between the bus blocks 70 and theelectrical bus assembly plate projection 71. Connections can then bemade to the electrical bus assemblies 60 for impressing an electricalcurrent to the electrolyzer. Also, connections can be then made fromsources of anolyte and catholyte (not shown) for providing feed of theserespective electrolytes to the anolyte feed port 24 and the catholytefeed port 25. Where desired, recirculation means can be provided forrecycled electrolyte from the troughs 35, 36 back through the feeds 24,25. Where desired, a hood may be included over the top of theelectrolyzer 20.

Although the representative electrolyzer 20 as shown in FIG. 3 isequipped with cells arranged in monopolar arrangement, it is to beunderstood that when the electrolyzer might be utilized in differentmanner, that other cell arrangement could be serviceable. Thus, it iscontemplated that the cells could be arranged as bipolar cells, whicharrangement would entail different bus connections from those depictedin FIG. 3. For the electrolyzer 20, the general material of constructionfor the cell box, i.e, for the floor 28, side walls 33, 34, outer andinner plates 21 and 22, can be polypropylene or other suitable material,such as polyvinylchloride (PVC), Halar™, Kynar™ and chlorinatedpolyvinylchloride. Such material as polypropylene is also serviceablefor providing the troughs 35, 36 as well as the feed and discharge ports23-27. Generally, the anode frame 49, catholyte feed manifold 31 andanode separator plate 39 are made of chlorinated polyvinylchloride.Other suitable materials for these elements include Halar™,polyethylene, PVC and polypropylene. For efficient electricalconductivity, the bus bar is copper as are the block members 64, 65. Thebolt and nut 66, 67 for the block can be stainless steel. Typically, anyrods, e.g., the anode locating rods 58 are of titanium or a metal suchas stainless steel, nickel or zirconium. Where the electrolyzer, inmonopolar cell arrangement, will be utilized with an aqueous metal-ioncontaining aqueous medium, generally containing ferric ion for reductionto ferrous ion, as might be present in ferric sulfate, the anode can bea dimensionally stable anode of a substrate metal such as titaniumcoated with an electrochemically active coating. Alternative materialscontemplated for the anode include tantalum. The separator will mostsuitably be a synthetic diaphragm, as more particularly discussedhereinbelow. The cathode for such representative metal ion reduction canbe likewise dimensionally stable, as by providing a cathode titaniummetal substrate coated with an electrochemically active coating.

It is contemplated that the cell in which the electrode 5 can beutilized will be any such cell for carrying on an electrochemicalreaction. The cells may have any arrangements of electrodes,compartments and separators, including membranes and diaphragms, as isknown in the art for electrochemical cell construction. Thus, asmentioned hereinbefore, although a monopolar cell design has beendepicted as representative of the present invention in FIG. 3, any othercell design is contemplated for utilizing the electrode 5. Likewise, itis contemplated that such electrode 5 may be generally useful in anelectrochemical cell as an anode, cathode or as both.

An electrochemical cell embodying the electrode 5 of the presentinvention can be particularly useful where the electrode 5 can be usedto enhance the rate for any mass transport limited, or kineticallyhindered electrochemical reaction. Representative of such reactionsinclude metal ion oxidation or reduction and organic reactions,including organic destruction. Of special interest is the metal ionreduction reaction where ferric ion is reduced to ferrous ion. Exemplaryof a cell accommodating such reduction is a cell electrochemicallyreducing the ferric ion of a metal chelate. Such chelate wherein theferrous ion is oxidized can have been employed in any absorption processwhere constituents, such as NO and SO₂, are scrubbed from a flue gas.The oxidized metal chelate, which is then in an inactive state, can beelectrochemically reduced for recycle to the absorption process.

With the electrode 5 of the present invention in such electrochemicalreduction process, it has been found that the cell can be divided intoanode and cathode compartments by a diaphragm separator. Heretofore thecell apparatus for such process has relied on membrane separation ofanode and cathode compartments. The present invention is thus in partdirected to cell apparatus wherein the anode and cathode compartmentsare separated by a diaphragm separator and the cathode compartmentutilizes the layered electrode 5 for reduction of ferric ion to ferrousion. The catholyte can comprise an absorbent solution containingoxidized inactive metal chelates from a process as hereinbeforedescribed. The catholyte may also contain additional ingredients such assulfites. The anolyte in such process of special interest comprisesgenerally an aqueous electrolytic solution. This is usually an acidicsolution, e.g., at a pH of 2-4, which is an aqueous anolyte medium.Preferred constituents for this anolyte include acid, such as sulfuricand phosphoric, or combinations such as an acid, e.g., sulfuric, with asalt, as supplied by sodium sulfate. More generally, the anolyte forthis special process typically has a pH maintained within a range fromabout 1 to about 7.

For this representative ferric ion reduction cell, the anode can be madeof metals including titanium. Advantageously for efficient celloperation, the anode is a dimensionally stable anode of a valve metalsubstrate, preferably titanium for economy, having an electrochemicallyactive coating, particularly one as more specially describedhereinbelow.

The cathode is then the electrode 5 as described hereinbefore. Suchcathode is preferably titanium, for economy, for both the core and themesh. Advantageously, both the mesh as well as at least a portion of thecore in contact with the mesh, are coated with an electrochemicallyactive coating such as discussed hereinbelow. For convenience, theoperative electrode such as the cathode in this ferric ion reductioncell, may be referred to herein as the "working electrode". In thisinstance, the anode is the "counter electrode" as such term is usedherein.

The separator for this representative ion reduction cell is then adiaphragm, as has been mentioned above. For the diaphragm in the cell, asynthetic, electrolyte permeable diaphragm can be utilized. Thesynthetic diaphragms generally rely on a synthetic polymeric material,such as polyfluoroethylene fiber as disclosed in U.S Pat. No. 5,606,805or expanded polytetrafluoroethylene as disclosed in U.S. Pat. No.5,183,545. Such synthetic diaphragms can contain a water insolubleinorganic particulate, e.g., silicon carbide, or zirconia, as disclosedin U.S. Pat. No. 5,188,712, or talc as taught in U.S. Pat. No.4,606,805. Of particular interest for the diaphragm is the generallynon-asbestos, synthetic fiber diaphragm containing inorganicparticulates as disclosed in U.S. Pat. No. 4,853,101. The teachings ofthis patent are incorporated herein by reference.

Broadly, this diaphragm of particular interest comprises a non-isotropicfibrous mat wherein the fibers of the mat comprise 5-70 weight percentorganic halocarbon polymer fiber in adherent combination with about30-95 weight percent of finely divided inorganic particulates impactedinto the fiber during fiber formation. The diaphragm has a weight perunit of surface area of between about 3 to about 12 kilograms per squaremeter. Preferably, the diaphragm has a weight in the range of about 3-7kilograms per square meter. A particularly preferred particulate iszirconia. Other metal oxides, i.e, titania, can be used, as well assilicates, such as magnesium silicate and alumino-silicate, aluminates,ceramics, cermets, carbon, and mixtures thereof.

A preferred diaphragm for the ferric ion reduction cell is a compressed,non-isotropic fibrous diaphragm marketed under the trademark "ELRAMIX".

In general, the diaphragm compression may be within the range of fromabout one ton per square inch up to about six tons per square inch, ormore, e.g., seven tons per square inch. However, such is more typicallyfrom about one to less than five tons per square inch. The diaphragmscan be heated during compression for fusing and compressing thediaphragms. Further details concerning these diaphragms are disclosed inU.S Pat. No. 5,246,559. The diaphragms can be treated with a surfactantprior to use. The treatment can be carried out in accordance with theprocedure set forth in the Bon U.S. Pat. No. 4,606,805, or in accordancewith the procedure set forth in the Lazarz et al U.S. Pat. No.4,252,878.

As representative of the electrochemically active coatings that may beapplied to an electrode are those provided from platinum or otherplatinum group metals or they can be represented by active oxidecoatings such as platinum group metal oxides, magnetite, ferrite, cobaltspinel or mixed metal oxide coatings. Such coatings have typically beendeveloped for use as anode coatings in the industrial electrochemicalindustry. They may be water based or solvent based, e.g., using alcoholsolvent. Suitable coatings of this type have been generally described inone or more of the U.S. Pat. Nos. 3,265,526, 3,632,498, 3,711,385, and4,528,084. The mixed metal oxide coatings can often include at least oneoxide of a valve metal with an oxide of a platinum group metal includingplatinum, palladium, rhodium, iridium and ruthenium or mixtures ofthemselves and with other metals. Further coatings include tin oxide,manganese dioxide, lead dioxide, cobalt oxide, ferric oxide, platinatecoatings such as M_(x) PT₃ O₄ where M is an alkali metal and x istypically targeted at approximately 0.5, nickel-nickel oxide and nickelplus lanthanide oxides.

It is contemplated that coatings will be applied to the electrode by anyof those means which are useful for applying a liquid coatingcomposition to a metal substrate. Such methods include dip spin and dipdrain techniques, brush application, roller coating and sprayapplication such as electrostatic spray. Moreover, spray application andcombination techniques, e.g., dip drain with spray application can beutilized. It will be appreciated that particularly with a dip coatingprocedure for the electrode 5, such will typically be carried out bydipping the electrode 5 into coating composition up to the top edge 8 ofthe mesh 1 of the electrode 5. Such procedure will not only coat themesh 1, but also the electrode core 4 up to the edge 8. Following any ofthe foregoing coating procedures, upon removal from the liquid coatingcomposition, the coated metal surface may simply dip drain or besubjected to other post coating technique such as forced air drying.

Typical curing conditions for electrocatalytic coatings can include curetemperatures of from about 300° C. up to about 600° C. Curing times mayvary from only a few minutes for each coating layer up to an hour ormore, e.g., a longer cure time after several coating layers have beenapplied However, cure procedures duplicating annealing conditions ofelevated temperature plus prolonged exposure to such elevatedtemperature, are generally avoided for economy of operation. In general,the curing technique employed can be any of those that may be used forcuring a coating on a metal substrate. Thus, oven coating, includingconveyor ovens may be utilized. Moreover, infrared cure techniques canbe useful. Preferably for most economical curing, oven curing is usedand the cure temperature used for electrocatalytic coatings will bewithin the range of from about 450° C. to about 550° C. At suchtemperatures, curing times of only a few minutes, e.g., from about 3 to10 minutes, will most always be used for each applied coating layer.

In addition to the coated electrode 5 being serviceable as describedhereinabove, such may be used in a cell which is typically amulti-compartment cell with diaphragm or membrane separators.

The following example shows a way in which the invention has beenpracticed but should not be construed as limiting the invention.

EXAMPLE

A flow-through, monopolar electrochemical test cell was used having onecathode chamber and one anode chamber. The cell consisted of a polyvinylchloride (PVC) box with internal dimensions of 5 inches deep×4 incheswide×3.5 inches long, a PVC anode chamber, a single layer mesh anode,and a multiple layer mesh cathode. The anode chamber was separated by adiaphragm porous separator, an ELRAMIX™ diaphragm having a weight perunit of surface area of 5.17 kg/square meter, a height of 6 inches, awidth of 4 inches and a thickness of 0.70 inch. The polymer fibers ofthe diaphragm were polytetrafluoroethylene polymer fibers. The inorganicparticulate was zirconia. The diaphragm was composed of 70 weightpercent of zirconia and 30 weight percent of polytetrafluoroethylene. Ithad been pressed at five tons per square inch.

Each of the cell cathodes was in a form as shown in FIG. 2. Each cathodehad a titanium mesh coated with an electrochemically active coating ofiridium oxide and using a solution of IrCl₃ dissolved in n-butanol andHCl. The coating was applied by dipping the titanium mesh wrapped platein the coating solution to fully immerse the mesh in the solution, thenremoving the cathode from the solution and baking in the manner asdescribed in Example 1 of U.S. Pat. No. 4,797,182, but without the finalextended heating. By coating in this manner, the lower 6 1/8 inch areaof the cathode plate was also coated. Before coating, the mesh wasetched for about 3-5 minutes in 20%, by weight, of HCl maintained at 95°C. The active mesh of the cathode was 24 layers of a fine, highlyflexible titanium mesh having an 0.007 inch (0.178 mm) strand width andan 0.005 inch (0.13 mm) strand thickness. The individual diamondapertures had an 0.125 inch (3.18 mm) LWD and an 0.066 inch (1.68 mm)SWD. The specific surface area of the 24 layers of this mesh was 2842square inches per square foot. A 61/8 inch wide strip of mesh waswrapped around a 12 inch×313/16 inch×0.060 inch titanium plate twelvetimes. The bottom of the strip coincided with the bottom of the plate.This plate distributor was expanded titanium mesh having 5/16 inch LWDand 3/16 inch SWD apertures. The total final width of the 24 layers ofmesh and the distributor was 4 inches, i.e., the mesh added 3/32 inch ofadditional width at each side edge of the plate. The mesh was spotwelded to the plate at four spots, the spots being in the pattern of a21/2 inch by 31/2 inch rectangle with one spot at each corner of therectangle. The total area of the spot welds was about 0.9% of the totalprojected area of one broad face of the mesh.

The anode for the test cell was an expanded titanium metal mesh 23/16inches×6 inches×0.060 inch. The anode was coated with anelectrochemically active coating of tantalum oxide and iridium oxide andusing an aqueous, acidic solution of chloride salts, the coating beingapplied and baked in the manner as described hereinbefore. The majorface of the anode was spaced about 3/8 inch from the diaphragm bypositioning in a PVC anode frame.

The anode chamber was filled with sulfuric acid of 0.25 weight percentconcentration at approximately 0.7 pH. The anolyte was not circulated.Agitation was provided by oxygen evolution at the anode. The cathodechamber and a supply tank were filled with 3750 milliliters (ml) ofelectrolyte. The electrolyte was a nearly saturated solution of ammoniumaluminum sulfate containing 3745 milligrams per liter (mg/l) of totaliron and 2010 mg/l of ferric (+3) iron with a pH of approximately 2. Thesupply tank was heated and stirred. Catholyte solution was therebymaintained at 60° C. to 67° C. The circulation rate was 1 liter perminute. The catholyte was circulated through the cathode compartment ofthe cell such that it entered the top of the cathode and exited thebottom. To insure electrolyte circulation through and not by, thecathode, one major face of the cathode was pressed against one wall ofthe electrolyzer by the anode chamber. The opposite major face wasagainst the diaphragm. This eliminated any gaps between the diaphragmand the cathode and between the cathode and the cell wall.

The catholyte level was maintained at 4.5 inches so that the activeprojected area of the cathode was 4 inches×4.5 inches giving a totalactive projected area of 18 square inches. A current of 4.4 amps wasimpressed upon the cell for 30 minutes to provide a current density onthe cathode of 35 amps per square foot (ASF) based on the projectedarea. The ferric iron (Fe+3) concentration was reduced from 2010 to 730mg/l. for a current efficiency of 104.7%. Ferric ion concentrations weredetermined by the HACH Titraver sodium periodate hand titration method.The current was then reduced to 3.1 amps (25 ASF) for another 20minutes. The ferric iron concentration was reduced to 260 mg/l for acurrent efficiency of 81.9%. Operating results are reported in the Tablebelow, where "NA" ans "not available".

                  TABLE                                                           ______________________________________                                        Time                                   Current                                  Minutes Amps ASF Cell Voltage V Fe.sup.+3 mg/l Efficiency %                 ______________________________________                                         0     4.4    35      5.6      2010    NA                                        5 4.4 35 4.84 1820  93.4                                                     10 4.4 35 4.67 1610  103.2                                                    15 4.4 35 4.61 1360  122.8                                                    20 4.4 35 4.63 1150  103.2                                                    25 4.4 35 4.65 970 88.5                                                       30 4.4 35 4.74 730 118                                                        35 3.1 25 3.82 580 103.2                                                      40 3.1 25 4.02 450 89.5                                                       45 3.1 25 4.03 360 61.9                                                       50 3.1 25 3.97 260 68.8                                                     ______________________________________                                    

We claim:
 1. An electrode comprising a core and an exterior wrappingmember, which core comprises a rigid metal core member, which coremember is in integral engagement with a layer of an exterior meshwrapping member from a strip of mesh wound around said core member,which mesh is a flexible metal mesh and said metal mesh wrapping memberlayer engages said metal core member in electrically conductive contact.2. The electrode of claim 1 wherein said core member is a rigid andsolid, planar metal member having front and back major faces and anedge, all in engagement with said exterior wrapping member.
 3. Theelectrode claim 1 wherein said core member provides rigid reinforcementmeans as well as electrical current distribution means for saidelectrode.
 4. The electrode of claim 1 wherein said electrode is ananode.
 5. The electrode of claim 4 wherein said anode comprises one ormore of a metal ion oxidation anode, an oxygen-evolving anode, or anorganic oxidation anode.
 6. The electrode of claim 4 wherein said anodecomprises a metal anode of a metal selected from the group consisting ofsteel, nickel, valve metal, or lead, and said anode is in the form of aplate, perforate member, rods or blades.
 7. The electrode of claim 6wherein said metal mesh is a valve metal mesh and the valve metal ofsaid core member and the valve metal of said mesh layer is selected fromthe group consisting of titanium, tantalum, niobium and zirconium, theiralloys and intermetallic mixtures.
 8. The electrode of claim 1 whereinsaid exterior wrapping member is, at least in part, flexed against, andheld in electrical contact with, said core member.
 9. The electrode ofclaim 1 wherein said exterior wrapping layer is pressed and secured inelectrical contact against said core member at least in part by welding.10. The electrode of claim 9, wherein said welding is spot welding andthe area of said spot welding is less than one percent of the projectedarea of said exterior wrapping member.
 11. The electrode of claim 1wherein said exterior wrapping member is present around a portion onlyof said core member.
 12. The electrode of claim 1 wherein said layer ofexterior mesh wrapping member consists of a layer of expanded metal,non-woven mesh.
 13. The electrode of claim 12 wherein said expandedmetal mesh has a pattern of substantially rhombus shaped voids havingLWD dimension within the range from about 0.1 inch to about 0.15 inch,SWD dimension within the range from about 0.04 inch to about 0.09 inch,and strand width within the range from about 0.003 inch to about 0.012inch.
 14. The electrode of claim 13 wherein said layer has a thicknesswithin the range of from about 0.0025 inch to about 0.025 inch.
 15. Theelectrode of claim 1 having at least a second layer of said mesh. 16.The electrode of claim 1 wherein said exterior wrapping member iscrimped around said core member.
 17. The electrode of claim 1 whereinsaid electrode has a potential for ferric ion reduction of greater than+0.1 volt versus a normal hydrogen electrode, when operating at 100%current efficiency.
 18. The electrode of claim 1 wherein more than onecontinuous strip of mesh is wound around said core and said strips areplaced edge-to-edge thereon.
 19. The electrode of claim 18 wherein saidmesh strips are spaced apart on said core.
 20. The electrode of claim 1wherein said wrapping member has an electrochemically active coating.21. The electrode of claim 20 wherein said electrochemically activecoating contains a platinum group metal, or metal oxide or theirmixtures.
 22. The electrode of claim 21 wherein said electrochemicallyactive coating contains at least one oxide selected from the groupconsisting of platinum group metal oxides, magnetite, ferrite, cobaltoxide spinel, and tin oxide, and/or contains a mixed crystal material ofat least one oxide of a valve metal and at least one oxide of a platinumgroup metal, and/or contains one or more of manganese dioxide, leaddioxide, platinate substituent, nickel-nickel oxide and nickel pluslanthanide oxides.
 23. The electrode of claim 1 wherein said core memberhas, on at least a part of said member, an electrochemically activecoating.
 24. An electrolytic cell containing the electrode of claim 1.25. The cell of claim 24 wherein said cell is a metal ion oxidation orreduction cell, or a cell for the destruction of organic compounds, or asalt splitting cell.